diff --git a/src/main/java/com/ieum/ict/ieum/IeumApplication.java b/src/main/java/com/ieum/ict/ieum/IeumApplication.java
index e4a503f..3f5b5f3 100644
--- a/src/main/java/com/ieum/ict/ieum/IeumApplication.java
+++ b/src/main/java/com/ieum/ict/ieum/IeumApplication.java
@@ -19,14 +19,18 @@ public static void main(String[] args) {
     CommandLineRunner seedAdminUser(UserRepository userRepository, PasswordEncoder passwordEncoder) {
         return args -> userRepository.findByEmail("admin@ieum.com").ifPresentOrElse(
                 user -> {
+                    if (user.getLoginId() == null) {
+                        user.updateLoginId("admin");
+                    }
                     if (user.getRole() != UserRole.ADMIN) {
                         user.updateRole(UserRole.ADMIN);
-                        userRepository.save(user);
                     }
+                    userRepository.save(user);
                 },
                 () -> {
                     User admin = new User(
                             "admin@ieum.com",
+                            "admin",
                             passwordEncoder.encode("admin1234!"),
                             "ieum_admin"
                     );
diff --git a/src/main/java/com/ieum/ict/ieum/admin/api/AdminUserResponse.java b/src/main/java/com/ieum/ict/ieum/admin/api/AdminUserResponse.java
index 7910a88..98d0e04 100644
--- a/src/main/java/com/ieum/ict/ieum/admin/api/AdminUserResponse.java
+++ b/src/main/java/com/ieum/ict/ieum/admin/api/AdminUserResponse.java
@@ -3,6 +3,8 @@
 import com.ieum.ict.ieum.auth.domain.User;
 import com.ieum.ict.ieum.auth.domain.UserRole;
 
-public record AdminUserResponse(Long id, String email, String name, UserRole role) {
-    public static AdminUserResponse from(User user) { return new AdminUserResponse(user.getId(), user.getEmail(), user.getName(), user.getRole()); }
+public record AdminUserResponse(Long id, String email, String loginId, String name, UserRole role) {
+    public static AdminUserResponse from(User user) {
+        return new AdminUserResponse(user.getId(), user.getEmail(), user.getLoginId(), user.getName(), user.getRole());
+    }
 }
diff --git a/src/main/java/com/ieum/ict/ieum/auth/api/AuthRequest.java b/src/main/java/com/ieum/ict/ieum/auth/api/AuthRequest.java
index 4bacbc0..fbcd68e 100644
--- a/src/main/java/com/ieum/ict/ieum/auth/api/AuthRequest.java
+++ b/src/main/java/com/ieum/ict/ieum/auth/api/AuthRequest.java
@@ -6,9 +6,11 @@
 
 public final class AuthRequest {
     private AuthRequest() {}
-    public record Signup(@NotBlank @Email String email, @NotBlank @Size(min = 8) String password,
+    public record Signup(@NotBlank @Email String email,
+                         @NotBlank @Size(min = 4, max = 30) String loginId,
+                         @NotBlank @Size(min = 8) String password,
                          @NotBlank String name) {}
-    public record Login(@NotBlank @Email String email, @NotBlank String password) {}
+    public record Login(@NotBlank String loginId, @NotBlank String password) {}
     public record Refresh(@NotBlank String refreshToken) {}
     public record Logout(@NotBlank String refreshToken) {}
 }
diff --git a/src/main/java/com/ieum/ict/ieum/auth/domain/User.java b/src/main/java/com/ieum/ict/ieum/auth/domain/User.java
index 87a7ade..b8c5494 100644
--- a/src/main/java/com/ieum/ict/ieum/auth/domain/User.java
+++ b/src/main/java/com/ieum/ict/ieum/auth/domain/User.java
@@ -14,6 +14,8 @@ public class User {
     private Long id;
     @Column(nullable = false, unique = true)
     private String email;
+    @Column(unique = true)
+    private String loginId;
     @Column(nullable = false)
     private String password;
     @Column(nullable = false)
@@ -25,19 +27,21 @@ public class User {
     @Column(nullable = false)
     private UserRole role = UserRole.USER;
 
-    public User(String email, String password, String name) {
+    public User(String email, String loginId, String password, String name) {
         this.email = email;
+        this.loginId = loginId;
         this.password = password;
         this.name = name;
     }
 
     public User(String email, String password, String name, AuthProvider authProvider) {
-        this(email, password, name);
+        this(email, null, password, name);
         this.authProvider = authProvider;
     }
 
     public void updateRefreshToken(String refreshToken) { this.refreshToken = refreshToken; }
     public void clearRefreshToken() { this.refreshToken = null; }
     public void updateRole(UserRole role) { this.role = role; }
+    public void updateLoginId(String loginId) { this.loginId = loginId; }
     public boolean isGoogleLogin() { return authProvider == AuthProvider.GOOGLE; }
 }
diff --git a/src/main/java/com/ieum/ict/ieum/auth/repository/UserRepository.java b/src/main/java/com/ieum/ict/ieum/auth/repository/UserRepository.java
index 22537db..6d7ae0b 100644
--- a/src/main/java/com/ieum/ict/ieum/auth/repository/UserRepository.java
+++ b/src/main/java/com/ieum/ict/ieum/auth/repository/UserRepository.java
@@ -6,5 +6,7 @@
 
 public interface UserRepository extends JpaRepository<User, Long> {
     boolean existsByEmail(String email);
+    boolean existsByLoginId(String loginId);
     Optional<User> findByEmail(String email);
+    Optional<User> findByLoginId(String loginId);
 }
diff --git a/src/main/java/com/ieum/ict/ieum/auth/service/AuthService.java b/src/main/java/com/ieum/ict/ieum/auth/service/AuthService.java
index 44f47a3..0f70924 100644
--- a/src/main/java/com/ieum/ict/ieum/auth/service/AuthService.java
+++ b/src/main/java/com/ieum/ict/ieum/auth/service/AuthService.java
@@ -26,14 +26,22 @@ public void signup(AuthRequest.Signup request) {
         if (userRepository.existsByEmail(request.email())) {
             throw new ResponseStatusException(HttpStatus.CONFLICT, "이미 가입된 이메일입니다.");
         }
-        userRepository.save(new User(request.email(), passwordEncoder.encode(request.password()), request.name()));
+        if (userRepository.existsByLoginId(request.loginId())) {
+            throw new ResponseStatusException(HttpStatus.CONFLICT, "이미 사용 중인 아이디입니다.");
+        }
+        userRepository.save(new User(
+                request.email(),
+                request.loginId(),
+                passwordEncoder.encode(request.password()),
+                request.name()
+        ));
     }
 
     public AuthResponse login(AuthRequest.Login request) {
-        User user = userRepository.findByEmail(request.email())
-                .orElseThrow(() -> new ResponseStatusException(HttpStatus.UNAUTHORIZED, "이메일 또는 비밀번호가 올바르지 않습니다."));
+        User user = userRepository.findByLoginId(request.loginId())
+                .orElseThrow(() -> new ResponseStatusException(HttpStatus.UNAUTHORIZED, "아이디 또는 비밀번호가 올바르지 않습니다."));
         if (!passwordEncoder.matches(request.password(), user.getPassword())) {
-            throw new ResponseStatusException(HttpStatus.UNAUTHORIZED, "이메일 또는 비밀번호가 올바르지 않습니다.");
+            throw new ResponseStatusException(HttpStatus.UNAUTHORIZED, "아이디 또는 비밀번호가 올바르지 않습니다.");
         }
         String accessToken = jwtTokenProvider.create(user.getEmail(), "access", user.getRole().name(), 3600000);
         String refreshToken = jwtTokenProvider.create(user.getEmail(), "refresh", user.getRole().name(), 1209600000);
@@ -75,7 +83,7 @@ public AuthResponse refresh(AuthRequest.Refresh request) {
     }
 
     public AuthResponse adminLogin(AuthRequest.Login request) {
-        User user = userRepository.findByEmail(request.email())
+        User user = userRepository.findByLoginId(request.loginId())
                 .filter(candidate -> candidate.getRole() == UserRole.ADMIN)
                 .orElseThrow(() -> new ResponseStatusException(HttpStatus.UNAUTHORIZED, "관리자 계정 정보가 올바르지 않습니다."));
         if (!passwordEncoder.matches(request.password(), user.getPassword())) {
diff --git a/src/main/java/com/ieum/ict/ieum/user/api/UserResponse.java b/src/main/java/com/ieum/ict/ieum/user/api/UserResponse.java
index f4c6437..dbf65d9 100644
--- a/src/main/java/com/ieum/ict/ieum/user/api/UserResponse.java
+++ b/src/main/java/com/ieum/ict/ieum/user/api/UserResponse.java
@@ -1,3 +1,3 @@
 package com.ieum.ict.ieum.user.api;
 
-public record UserResponse(Long id, String email, String name) {}
+public record UserResponse(Long id, String email, String loginId, String name) {}
diff --git a/src/main/java/com/ieum/ict/ieum/user/service/UserService.java b/src/main/java/com/ieum/ict/ieum/user/service/UserService.java
index 06b99f6..0a5ff54 100644
--- a/src/main/java/com/ieum/ict/ieum/user/service/UserService.java
+++ b/src/main/java/com/ieum/ict/ieum/user/service/UserService.java
@@ -16,6 +16,6 @@ public class UserService {
     public UserResponse getMyInfo(String email) {
         User user = userRepository.findByEmail(email)
                 .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "사용자를 찾을 수 없습니다."));
-        return new UserResponse(user.getId(), user.getEmail(), user.getName());
+        return new UserResponse(user.getId(), user.getEmail(), user.getLoginId(), user.getName());
     }
 }